1. Field of the Invention
The present invention relates to an apparatus and method to produce steam, gas and solid waste without wastewater discharge. Low quality fuel and water are used in the direct contact heat exchange process. The procedure is carried out inside a rotating pressurized vessel.
2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 37 CFR 1.98
Generally, steam production facilities are divided into two main types: direct contact steam production facilities, and indirect steam facilities steam production facilities. In direct contact steam production facilities, water is mixed with hot gases to produce steam through direct heat exchange between the water and the gases. The end result is a mixture of steam and gas. In an indirect steam production facility, heat that is required to produce the steam from the water is supplied through a metal wall, typically a steel wall that prevents the mixture of the water and hot gases and allows a difference in pressure between the steam and combustion sides. Indirect contact steam generation is widely used for steam production. The devices vary from steam drum boilers to Once-Through Steam Generators (OTSG). The heat exchange can be by radiation, convection or both.
Direct-contact steam generators are much more limited in use than non-direct contact steam generators. One of the proven applications for the direct contact steam generation process is enhanced oil recovery (EOR), wherein steam and flue gas (mainly CO2) mixtures are injected into a heavy oil reservoir to increase oil mobilization in heavy oil production.
The main characteristic of the direct contact steam generator is that the produced steam contains impurities, such as combustion products (mainly gases and possible solids) that were burned during steam production. Those gases are mainly carbon dioxide and nitrogen, when air is used for stoichiometric combustion processes. Additional gases can be present in smaller percentages, such as CO, SOx, NOx and other gases. Due to the presence of combustion gases, the steam produced in direct contact will be used by open circuit systems or by systems that can handle the impurities in the steam.
The need for the present invention is driven by challenges facing the heavy oil production industry involved with enhanced oil recovery (EOR) and especially the negative environmental effect of that such oil development. For example, steam assisted gravity drainage (SAGD), cyclic steam stimulation (CSS) and open mining of tar sands generates large amounts of waste water and CO2 emissions. The disadvantages of the prior art direct contact steam generators prevented them from becoming preferred commercial solutions for EOR. As a result, indirect steam generators, mainly OTSG and steam boilers, are used commercially used. In the prior art, the systems of both direct and indirect steam generators have a continuous flow of water through them that maintains a solids concentration at acceptable levels in the steam vessel. Additionally, the flow of water controls solids build-up in the steam reactor for direct generators and in the drums or inside the tubes for indirect generators. The dissolved solids concentration increases in the steam reactor, as more water transitions from liquid to gas throughout the process. The water with the largest amount of concentrated solids is rejected from the steam generation process to crystallized treatment facilities or disposal wells. Thus, there is a need to eliminate the use of these additional treatment facilities for conversion of the waste into solid form.
The prior art of down-hole direct contact steam generators does not disclose continuous water flow through the system to remove the solids. However, the generated solids are released to a reservoir. These prior art systems are limited to the use of clean fuels and require clean water, since impurities and generated solids can block the reservoir.
There is also a need to utilize low quality carbon fuel such as coal, coke, and asphaltin as the energy source for steam production in the heavy oil production industry to replace the widespread use of natural gas. Natural gas is a clean and valuable resource that, from a public perspective, should not be used for steam production in heavy oil extraction. This clean resource should be preserved and used for residential purposes. The present invention can work with natural gas or other clean liquid/gas fuels, however, due to its ability to handle the solids both from the water and the fuel and remove SO2, the use dirty fuel and water is preferred.
There is a major need to produce steam in a thermally efficient facility.
There is a need to use low quality water that contains solids including: silica clay from tailing ponds, dissolved solids and organic emulsions, (like tar and heavy oil-based materials),
There is a need for low-quality water to be used directly, with minimal additional treatment prior to steam production.
There is a need to extract the continuously produced waste in a dry solid form that can be efficiently and economically disposed of in a landfill.
Above all, there is a need for an apparatus and process that will enable fulfilling the above-mentioned needs in a simple and reliable way.
Various patents have been issued that are relevant to the present invention. For example, U.S. Pat. No. 2,916,877, issued on Dec. 15, 1959 to Walter, teaches a pressure fluid generator, which utilizes direct-contact heat transfer. The pressure fluid generator is in the form of an elongated combustion chamber. A coolant in the heat exchange relationship is injected into the combustion chamber to form with the combustion products therein, as a gas and superheated vapor-working mixture at a relatively high temperature and pressure. Some embodiments include in-line soot filters and circulated water, and the fuel is hydrocarbon gas.
U.S. Pat. No. 4,398,604, issued on Aug. 16, 1983 to Krajicek et al. describes a system for aboveground stationary direct contact horizontal steam generation. The method and apparatus produces a high-pressure thermal vaporized stream of water vapor and combustion gases for recovering heavy viscous petroleum from a subterranean formation. High-pressure combustion gases are directed into a partially water-filled vapor generator vessel to produce a high-pressure stream of water vapor and combustion gases. The produced solids are continually removed with reject water.
There are also patents relating to applications in heavy oil production. U.S. Pat. No. 4,463,803, issued to Wyatt on Aug. 7, 1984 describes a system for down-hole stationary direct contact steam generation for enhanced heavy oil production. The method and apparatus generate high-pressure steam within a well bore. The steam vapor generator is constructed for receiving and mixing high-pressure water, fuel and oxidants in a down-hole configuration. The produced solids are discharged to the oil reservoir.
Various patents have disclosed rotational elements of steam generators. U.S. Pat. No. 1,855,819, issued on Apr. 26, 1932 to Blomquist et al. describes a rotary boiler, where the pressure chamber is rotating inside the combustion area while producing the steam in an adjacent indirect heat exchanger. To increase the efficiency of the invention, Blomquist used scraper chains within the steam generating tubes, to prevent the sludge from adhering to the tubes interior walls. British patent No. 0 328 339, issued on May 1, 1930 to Kalabin teaches a direct contact steam generator with a rotating pressure vessel. The gasses flow to a rotating chamber, where they are mixed with air and combusted completely. Water covers the walls of the rotating chamber. This is achieved by the centrifugal force of the rotating chamber, exposing the water to gas combustion.
Various patents have disclosed rotating drums with chains as heat exchange elements. These are designed to capture heat from the combustion gas and transfer it to the liquid or slurry medium. U.S. Pat. No. 1,313,281, issued on Aug. 19, 1919 to Fasting describes a rotary kiln for slurry material. The chains lift the slurry onto the path of the hot combustion products, to increase the heat transfer and slurry evaporation. U.S. Pat. No.4,207,290, issued on Jun. 10, 1980 to Lee, discloses a flue gas scrubber. The elongated tubular drum scrubber, fitted with chains as means of heat transfer, is used for increasing the direct contact between lime slurry and sulfur rich flue gas. The rotating scrubber has two main areas: a scrubbing area with liquid slurry and a drying area. In the drying area, the heat from the flue gas evaporates the moisture to generate dry pellets.
The use of a rotating drum drier with chains is common as a method of heat transfer in several industries. For example, the pulp and paper industry. In the aforementioned application, the products are the solids. The liquids and moisture are driven out of the product and released to the environment, close to atmospheric pressure. In many cases, the heat from the produced solids is used to pre-heat the combustion air. Usually, excessive water within the solids results in severe energy wastes and high fuel costs, due to the expensive process of drying and loosing the liquids.
The use of rotating kiln with chains as a means of heat exchange has been an industrial standard since the beginning of the 19th century. (See The Rotary Cement Kiln by Peray and Waddell, Published 1972, paragraph 1.3 and 3.5.). The use of chains for internal heat exchangers became popular with kiln operators because of their simplicity and ease of operation. In wet processes, a feed enters the cement kiln in the form of slurry with approximately 30% moisture content. The slurry temperature is approximately 38° C. as it enters the chains. The temperature rises to 200-260° C. when it leaves the chains. The slurry helps reduce the dust. In a dry kiln, the feed is in powder form. The temperature in the chain section increases the feed temperature to 565-705° C. In this section, the mixture is partially calcined.
It is an objective of the present invention to provide an apparatus and method for the production of high pressure, dry, super-headed steam and a combustion gas mixture using direct contact heat transfer between available water and combustion gases in a rotating reactor.
It is another object of the present invention to provide an apparatus and method where the waste solids generated by combustion and steam generation are carried by gravity to regenerated surfaces at the bottom of the apparatus. These regenerated surfaces are chains that hang in the rotating vessel of the apparatus. The chains act as heat transfer media and they remove deposits and build-ups of waste solids.
It is another object of the present invention to provide an apparatus and method where the waste solids are separated and removed in the form of dry particles or high concentrated slurry from the rotating steam generator by carry gas mixture, without decreasing the steam-gas mixture pressure and temperature.
It is another object of the present invention to provide an apparatus and method that produces steam from low-quality tailing pond and reject-water containing high levels of dissolved inorganic solids or organic solids. All liquid water is converted to steam and no liquid is discharged from the apparatus.
It is another object of the present invention to provide an apparatus and method that produces steam from low-quality fuel containing inorganic impurities. For example, coal, coke, asphaltin or any other available carbon based fuel, wherein the combustion byproducts of this fuel are slag and ash in solid form.
It is another objective of the present invention to provide an apparatus and method that minimizes the amount of energy used to produce the mixture of steam and gas that is injected into underground formation to recover heavy oil.
It is a further objective of the present invention to provide an apparatus and method where the low quality water is converted to steam, without any wastewater flow.
It is another objective of the present invention to provide a process that produces pressurized high-temperature steam and gas in a rotating drum. Solids are removed in dry form from the rotating drum. The hot gas flow and the remaining solids are injected into a vessel, where the solids are scrubbed by liquid water. A saturated, wet, steam and combustion gas is produced. Water with solids continually recycled back from the vertical vessel to the rotating steam generator. The saturated wet steam-gas mixture is used for enhanced oil recovery processes.